The invention relates to an arrangement and a method for protecting a multiple voltage supply system against voltage coupling between a high-voltage plane and a low voltage plane or against a pole reversal.
A device and a method for the arc-over protection of a single voltage supply system is known from DE 197 10 073 A 1. An arc-over protection device for protecting the electrical consumers or loads located in the supply system is connected in parallel with the generator output. The arc-over protection device contains a limiting unit for the supply system. The threshold value for the limiting unit is above the value for the generator voltage. If the supply system voltage exceeds this threshold value, the generator output is clamped at the threshold value with the aid of a parallel-connected sacrificial consumer and the generator voltage is simultaneously adjusted or regulated down. As a result, sensitive semiconductor elements are protected against supply system arc-over.
With supply systems in several voltage planes, for example, a two-voltage supply system 42 V/14 V, voltage arc-over, short-circuits or pole reversals between two voltage planes of the supply system can occur in addition to short-circuits of the individual supply systems toward ground. The time history and the absolute values of the voltages in the different voltage planes of the supply system depend on many factors during the voltage arc-over between voltage planes. Among other things, these factors include the number, size, type and technological level of the batteries used in the supply system, as well as their charging state and aging condition. Furthermore included are the type and number of contact resistances and power resistances in the supply system, the number and type of elements connected between the voltage planes and the intensity and location of the voltage arc-over in the supply system. In particular the location of an unintended voltage coupling in the supply system greatly influences the resulting voltage distribution. Owing to the fact that the location of a voltage coupling or short-circuit in the supply system cannot be predicted, the results of a voltage arc-over between the voltage planes in known multiple voltage supply systems cannot be predicted either. To be sure, the individual voltage planes normally are protected against a short circuit to ground, but this protection does not provide any or only insufficient help in case of a short circuit between the voltage planes. This is particularly important for motor vehicles having safety-relevant control devices, such as ESP (external power source) control devices, airbag control devices, ABS (anti-locking system) control devices, the reliable operation of which must be ensured even in the case of a voltage arc-over. Depending on the locally adjusting voltage potential, consumers connected to the supply system can be placed in a state of over voltage or undervoltage, depending on their layout for low voltage or high voltage. In the case of the previously mentioned, safety-relevant control devices, an operational loss must then be expected for these control devices.
If a high-voltage battery is installed in the high-voltage plane and a low-voltage battery in the low-voltage plane, an uncontrolled voltage arc-over between the two voltage planes of the supply system becomes even more dangerous. As a result of the coupling between two batteries from different voltage planes, high compensating currents can flow that can destroy all components of the supply system, including the batteries themselves.
For example, if the high-voltage plane is connected due to a short circuit to a line of the low-voltage plane and to a MOS semiconductor switch and the load triggered by this switch in the low-voltage plane, then the normally existing inverse diode of the MOS switch is destroyed and the connected load will switch on without control. This can lead to unpredictable driving conditions for motor vehicles in particular, depending on the type of load that is activated without control, which cannot be tolerated.
The same, previously described dangers also arise if a high-voltage system component is connected to the low-voltage plane, for example as a result of pole reversal or confusion. The danger of confusing the planes always exists, for example, during the external charging of motor vehicle batteries or if an external starting aid is used.
Thus, it is the object of this invention to provide better protection for multiple voltage supply systems against uncontrollable voltage coupling between the different voltage planes of the supply system.
The above object is achieved according to the present invention by an arrangement for protecting a multiple voltage supply system against voltage coupling between a high-voltage plane and a low voltage plane or against a pole reversal, with the high voltage plane including a high voltage battery, a controllable generator connected to the high voltage battery, and at least one high voltage load connected to the battery and the generator, and with the low-voltage plane including a low voltage battery and at least one load connected to the low voltage battery, and with the arrangement comprising: a voltage-limiting unit connected, as to potential, between battery in the low-voltage plane and electrical ground to limit the voltage at the low voltage plane; a normally closed controllable battery disconnect switch connected in the high-voltage plane to disconnect the high voltage battery from the generator and the at least one load when opened; and, control signal lines connecting control terminals of the voltage-limiting unit, the battery disconnect switch and the generator to each other; and wherein the voltage limiting unit includes circuit means for, upon detection of an undesirable voltage coupling from the high-voltage plane to the low-voltage plane, keeping the voltage in the low-voltage plane constant, and for transmitting a signal via the signal lines (a) to the battery disconnect switch to open the switch and separate the high-voltage plane from the high-voltage battery, and (b) to the control terminal of the generator and to adjust the output voltage of the generator down.
Generally, in the above case of a voltage coupling between the high-voltage plane and the low-voltage plane, the above object is solved by clamping the voltage in the low-voltage plane of the supply system with a voltage limiter to remain at the low-voltage value until a battery disconnect switch in the high-voltage plane of the supply system is opened and the generator in the high-voltage plane is adjusted down at its output, at least to the voltage value of the low-voltage plane. An even higher operational safety is achieved for the low-voltage plane in that the generator output is adjusted down completely. As a result, the high-voltage plane of the supply system is disconnected from the high-voltage sources. The voltage in the low-voltage plane is furthermore prevented from rising, even in case of a short circuit between the two voltage planes of the supply system, and the consumers in the low-voltage plane can continue to be operated safely.
The following advantages are achieved with the invention.
Motor vehicles are equipped with two-voltage supply systems to provide high-performance consumers, e.g., rear window heaters, seat heaters, heating systems in addition to the engine heating, electrical drive motors etc., with a high-voltage plane, while electronic control devices, which are primarily configured with semiconductor elements, can continue to be supplied by a second low-voltage plane. In addition, two-voltage supply systems offer the advantage of an optional second and redundant backup plane for safety-relevant functions in motor vehicles, such as ESP systems, ABS systems or airbag control devices if one voltage plane in the supply system fails.
With the invention, it is possible to protect a second low-voltage plane not only against a short circuit to ground, but also against a possible voltage coupling between the different voltage planes of a multiple voltage supply system. As a result, the invention advantageously permits connecting the safety-relevant electrical and electronic components of a motor vehicle in the low-voltage plane and to further improve the operational safety of the motor vehicle by protecting the low-voltage plane.
If external supply sources are connected to multiple voltage supply systems, for example for charging up the battery in the high-voltage plane, the danger exists that the external high-voltage source is accidentally connected to the low-voltage plane of the supply system. Extensive damage, particularly to semiconductor components, must then be feared in traditional two-voltage supply systems, which would result in extensive repairs. In that case, the invention advantageously protects the low-voltage plane of the supply system against such pole reversal damage.
Present-day motor vehicle supply systems have a supply system management, which distributes the available power reserves to the system consumers on the basis of a priority list. Known supply systems therefore have a supply system control device, which can purposely switch the consumers in the supply system on and off. This functionality of a supply system control device is also used for multiple voltage supply systems. In connection with the invention, the functionality of known supply system control devices can advantageously be expanded to narrow down the location of the undesirable arc-over in the supply system in case of a voltage coupling between the two voltage planes of a two-voltage supply system. For this, the complete high-voltage plane of the supply system with all consumers and power branches is initially turned off. Following this, the individual power branches in the high-voltage plane are switched on by the supply system, one after another, in accordance with a priority list. Following each switch-on of a power branch in the high-voltage plane, the voltage-limiting unit in the low voltage plane simultaneously, and parallel thereto, conducts a check as to whether the voltage in the low-voltage plane increases above the permissible nominal value. If the voltage in the low-voltage plane increases above this nominal voltage inclusive of a tolerance range, the undesirable voltage arc-over or short circuit must be searched for between the two voltage planes, in the last power branch switched on by the supply system in the high-voltage plane. As a result, the multiple voltage supply system has a diagnostic capability and the supply system control device is expanded by a diagnostic function for localizing undesirable voltage arc-over between the different voltage planes of the supply system.
Exemplary embodiments of the invention are explained in further detail in the following with the aid of drawings.